docs: example for NATS cluster

[mdelapenya]

What does this PR do?

It adds a testable example for the creation of a NATS cluster, which includes:

• a docker network in which the containers will live. Then, containers can resolve by hostname/alias in the network
• three NATS containers properly configured for the cluster setup
• NATS client configured with the servers URL
• some example operations for interacting with the cluster (subscribe, unsubscribe, etc)

This PR finally updates the current docs, as the WithArgument option was missing:

• Render URL for the docs: https://deploy-preview-2591--testcontainers-go.netlify.app/modules/nats/#nats-cluster

Why is it important?

Show by example how to set up a NATS cluster without adding anything to the current API, just configuring it properly.

Related issues

• Closes #2393

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[mdelapenya]

@bearrito could you please take a look at this? 🙏

[mdelapenya]

I'm going to merge this one, @bearrito please reopen the original issue in case you have any other consideration.